Method and apparatus for providing a gas correlation filter for remote sensing of atmospheric trace gases
| Title: | Method and apparatus for providing a gas correlation filter for remote sensing of atmospheric trace gases |
|---|---|
| Patent Number: | 7,050,215 |
| Publication Date: | May 23, 2006 |
| Appl. No: | 10/634103 |
| Application Filed: | August 01, 2003 |
| Abstract: | A correlation filter is provided having passbands at wavelengths corresponding to the absorption spectrum of an atmospheric gas of interest. In particular, the correlation filter features narrow, non-linearly spaced passbands having center wavelengths that are correlated to the non-linearly spaced absorption lines of an atmospheric gas. A correlation filter in accordance with an embodiment of the present invention includes a compensation stack having a number of thin film layers, at least some of which have an optical thickness that is not equal to an integer multiple of one-quarter of a wavelength of an absorption line of the gas of interest. The correlation filter may be provided in association with an etalon, or may comprise a number of optical cavities. In accordance with an embodiment of the present invention, a number of absorption lines associated with an atmospheric gas may be simultaneously viewed, providing a signal indicating the presence and quantity of such gas in the atmosphere having a high signal-to-noise ratio. |
| Inventors: | Johnson, Brian R. (Superior, CO, US); Kampe, Thomas Ulrich (Boulder, CO, US) |
| Assignees: | Ball Aerospace & Technologies Corp. (Boulder, CO, US) |
| Claim: | 1. A correlated filter device, comprising: a compensation stack including a plurality of layers, wherein an optical thickness of at least some of said layers of said compensation stack does not equal an integer multiple of one-quarter of a wavelength of light having a first wavelength corresponding to a first passband of said filter device having a first center wavelength, wherein said filter device further comprises a second passband having a second center wavelength and a third passband having a third center wavelength, wherein said first center wavelength is separated from said second center wavelength by a first amount and wherein said second center wavelength is separated from said third center wavelength by a second amount that is not equal to said first amount. |
| Claim: | 2. The device of claim 1 , wherein said optical thickness of a layer comprises a distance equal to a thickness of said layer multiplied by an index of refraction of said layer. |
| Claim: | 3. The device of claim 1 , wherein said first wavelength is a wavelength of light in a vacuum. |
| Claim: | 4. The device of claim 1 , further comprising: an optical cavity. |
| Claim: | 5. The device of claim 4 , further comprising a reflective stack including a plurality of layers, wherein said compensation stack is associated with a first reflective surface of said optical cavity, and wherein said compensation stack comprises a second reflective surface of said optical cavity. |
| Claim: | 6. The device of claim 4 , wherein said optical cavity has an optical thickness greater than ten of said first wavelengths. |
| Claim: | 7. The device of claim 4 , wherein said optical cavity comprises an etalon. |
| Claim: | 8. The device of claim 7 , wherein said etalon comprises at least one of a Silicon etalon and a Germanium etalon. |
| Claim: | 9. The device of claim 7 , wherein said etalon comprises a Silicon etalon and has a thickness of about 386.5 mm. |
| Claim: | 10. The device of claim 1 , further comprising: a plurality of optical cavities. |
| Claim: | 11. The device of claim 10 , wherein at least some of said optical cavities are formed as layers within said compensation stack. |
| Claim: | 12. The device of claim 10 , wherein said plurality of optical cavities comprise layers within a filter having an optical thickness at least as great as one-half of said first center wavelength. |
| Claim: | 13. The device of claim 1 , wherein said compensation stack comprises high index of refraction layers formed from Germanium and low index of refraction layers formed from Silicon Monoxide. |
| Claim: | 14. The device of claim 1 , further comprising: a bandpass filter. |
| Claim: | 15. A system for sensing atmospheric trace gases, comprising: at least a first optical cavity; a first reflective stack forming a first reflective surface of said optical cavity, said first reflective stack including a plurality of thin film layers, wherein at least one of said thin film layers bas an optical thickness that is not equal to one quarter of a wavelength of light at a first passband of said system; a second reflective stack forming a second reflective surface of said optical cavity, wherein said first reflective stack comprises a compensation stack, wherein passbands of said system are not regularly spaced, and wherein said second reflective stack comprises a bandpass filter. |
| Claim: | 16. The system of claim 15 , wherein said at least a first optical cavity comprises an etalon having an optical thickness greater than about ten times said wavelength of light at said first passband of said system. |
| Claim: | 17. The system of claim 16 , wherein said etalon comprises at least one of a Silicon and a Germanium etalon. |
| Claim: | 18. The system of claim 15 , wherein said system includes at least six passbands, and wherein each of said six passbands is centered at an absorption line of an atmospheric gas. |
| Claim: | 19. The system of claim 18 , wherein said atmospheric gas comprises one of Carbon Monoxide and Carbon Dioxide. |
| Claim: | 20. The system of claim 15 , wherein said first reflective stack comprises Germanium high index of refraction layers and Silicon Monoxide low index of refraction layers. |
| Claim: | 21. The system of claim 15 , further comprising a detector, wherein light having a wavelength within said first passband, a second passband, and a third passband of said system is received at said detector, and wherein said first, second, and third passbands are separated from one another by different amounts. |
| Claim: | 22. A system for sensing atmospheric trace gases, comprising: a correlation filter including: a plurality of thin film layers, wherein said thin film layers include a plurality of high index of refraction layers and a plurality of low index of refraction layers, wherein at least some of said thin film layers have an optical thickness that is not equal to a quarterwave of light having a first wavelength corresponding to a center wavelength of a first passband of said correlation filter; and a plurality of optical cavities, wherein said system includes at least six passbands, and wherein each of said six passbands is centered at an absorption line of an atmospheric gas. |
| Claim: | 23. The system of claim 22 , wherein said plurality of optical cavities comprise thin film layers having an optical thickness of at least one-half a wavelength of said first wavelength. |
| Claim: | 24. The system of claim 22 , wherein passbands of said system are not regularly spaced. |
| Claim: | 25. The system of claim 22 , further comprising: a substrate, wherein said compensation stack is interconnected to a first surface of said substrate. |
| Claim: | 26. The system of claim 24 , further comprising: a bandpass filter stack, including a plurality of high index of refraction thin film layers and a plurality of low index of refraction thin film layers interconnected to a second surface of said substrate. |
| Claim: | 27. The system of claim 22 , wherein said atmospheric gas comprises one of Carbon Monoxide and Carbon Dioxide. |
| Claim: | 28. The system of claim 22 , wherein said high index of refraction layers comprise Germanium and said low index of refraction layers comprise Silicon Monoxide. |
| Claim: | 29. A system for sensing atmospheric trace gases, comprising: a correlation filter including: a plurality of thin film layers, wherein said thin film layers include a plurality of high index of refraction layers and a plurality of low index of refraction layers, wherein at least some of said thin film layers have an optical thickness that is not equal to a quarterwave of light having a first wavelength corresponding to a center wavelength of a first passband of said correlation filter; and a plurality of optical cavities, further comprising a detector, wherein light having a wavelength within said first passband, a second passband, and a third passband of said system is received at said detector, and wherein said first, second, and third passbands are separated from one another by different amounts. |
| Claim: | 30. The system of claim 29 , wherein said plurality of optical cavities comprise thin film layers having an optical thickness of at least one-half a wavelength of said first wavelength. |
| Claim: | 31. The system of claim 29 , wherein passbands of said system are not regularly spaced. |
| Claim: | 32. The system of claim 29 , further comprising: a substrate, wherein said compensation stack is interconnected to a first surface of said substrate. |
| Claim: | 33. The system of claim 29 , further comprising: a bandpass filter stack, including a plurality of high index of refraction thin film layers and a plurality of low index of refraction thin film layers interconnected to a second surface of said substrate. |
| Claim: | 34. The system of claim 29 , wherein each of said first, second and third passbands is centered at an absorption line of an atmospheric gas. |
| Claim: | 35. The system of claim 34 , wherein said atmospheric gas comprises one of Carbon Monoxide and Carbon Dioxide. |
| Claim: | 36. The system of claim 29 , wherein said high index of refraction layers comprise Germanium and said low index of refraction layers comprise Silicon Monoxide. |
| Current U.S. Class: | 359/260 |
| Patent References Cited: | 3432239 March 1969 Holland 3501641 March 1970 Krause 3802777 April 1974 Regnler et al. 3824018 July 1974 Crane, Jr. 3939348 February 1976 Barrett 3998552 December 1976 Stewart et al. 4035643 July 1977 Barrett 4057319 November 1977 Ash et al. 4195931 April 1980 Hara 4377324 March 1983 Durand et al. 4400058 August 1983 Durand et al. 4509857 April 1985 Vermande 4553816 November 1985 Durand et al. 4583855 April 1986 Bareket 4615033 September 1986 Nakano et al. 4729658 March 1988 Poultney 4743114 May 1988 Crane, Jr. 4930131 May 1990 Sizer, II 4937447 June 1990 Barrett 4962319 October 1990 Leonard et al. 4973853 November 1990 Leonard et al. 5088815 February 1992 Garnier et al. 5144498 September 1992 Vincent 5159406 October 1992 Adler et al. 5208654 May 1993 Shao et al. 5212585 May 1993 Ning 5214484 May 1993 de Mollerat du Jeu 5218426 June 1993 Hall et al. 5339155 August 1994 Partridge et al. 5539517 July 1996 Cabib et al. 5539518 July 1996 Bennett RE35355 October 1996 Ryan et al. 5606419 February 1997 Foosnaes et al. 5666225 September 1997 Colbourne 5719989 February 1998 Cushing 5731889 March 1998 Jeong et al. 5801831 September 1998 Sargoytchev 5835214 November 1998 Cabib et al. 5999322 December 1999 Cushing 6046854 April 2000 Bhagavatula 6075597 June 2000 Olshausen 6118421 September 2000 Kawaguchi et al. 6163380 December 2000 Hays 6243170 June 2001 Ershov 6268944 July 2001 Szapiel 6504971 January 2003 Margalit et al. 6522469 February 2003 Fuqua et al. 6545739 April 2003 Matsumoto et al. 2002/0191268 December 2002 Seeser et al. 2003/0011760 January 2003 Vaez-Iravani et al. 2003/0048985 March 2003 Hulse |
| Other References: | William S. Heaps et al., “Fabry-Perot Interferometer for col. CO2,” NASA Goddard Space Flight Center, 6 pages (Jun. 2002). cited by other E. Serabyn et al., “Dual Fabry-Perot Filter for Measurement of CO Rotational Spectra: Design and Application to the CO Spectrum of Venus,” Applied Optics, vol. 39, No. 34 (Dec. 1, 2000), pp. 6448-6452. cited by other Jerzy Closek, “Narrow-Band Interference Filters with Unconventional Spacer Layers,” Applied Optics, vol. 39, No. 1 (Jan. 1, 2000), pp. 135-140. cited by other P.L. Land et al., “High-Transmission Comblike Optical Filters,” J. Opt. Soc. Am. A, vol. 12, No. 3 (Mar. 1995), pp. 611-622. cited by other |
| Assistant Examiner: | Thomas, Brandi |
| Primary Examiner: | Mack, Ricky L. |
| Attorney, Agent or Firm: | Sheridan Ross P.C. |
| Accession Number: | edspgr.07050215 |
| Database: | USPTO Patent Grants |
| Language: | English |
|---|